Manufacture of abrasives



May 22, 1945. R. p CARLTQN 2,376,343

MANUFACTURE OF ABRASIVES Filed July 28, 1942 3 Sheets-Sheet 1 [nven/Zor wwwm AZZorn/eys y 1945 R. P. CARLTCN MANUFACTURE OF ABRASIVES 3 Sheets-Sheet 2 Filed July 28, 1942 A550 qys y 1945- R. P. CARLTON MANUFACTURE OF ABRASIVES Filed July 28, 1942 3 Sheets-Sheet 3 In emior Patented May 22, 1945 2,376,343 MANUFACTURE OF ABRASIVES Richard Paul Carlton, St. Paul, Minn., assignor to Minnesota Mining & Manufacturing Company, St. Paul, Minn, a corporation of Delaware Application July 28, 1942, Serial No. 452,632

6 Claims.

This invention relates in general to coated articles and to the art of coating, and more particularly to an improved method of and apparatus for applying pulverulent coatings to suitably adhesively coated surfaces, and while the invention finds particular utility in the art of making flexadhesive substance, such as animal or vegetable glue, or where a waterproof article is desired, the backing may be coated with any of the now well known waterproof adhesives of the Okie Patents 1,565,027, 1,565,028, of December 8, 1925, or 1,581,657 of April 20, 1926, for this purpose, and while the coating is still wet or unset, a suitable abrasive material such as garnet, corundum, sand or the like is applied thereto. The grains of abrasive substances are usually applied by gravity upon the upper adhesive coated surface of the backing, and they lie in the adhesive material in haphazard fashion due to the elongated nature of the abrasive particles, and in a large degree, the facets or cutting edges of the individual grains or grits often lie flat upon or are embedded in the adhesive coating in such a manner that in some instances their best cutting edges never come into contact with the work or at best are brought inefficiently into contact therewith. The invention here has as one of its objects to measurably increase the number of grits whose longer or.

gravity. As the grits pass through the intervening air space, there will be caused some change in their positions en route to the sheet or backing, but ordinarily neither the velocity given to the grits nor the eflect'of the air on them is sulficient to cause them to become aligned so as to assume positions substantially perpendicular to the backing. It is, therefore, necessary that independent force b applied to the grits, and I have found that by passing the grits through a static field of electric energy or of electro-magnetic energy or by mechanically imparting this force to the grits a much greater number of the individual particles will assume erect positions on the backing, which will enhance its cutting ability. As will later appear, my invention, in its several forms, is capable of application for operation in conjunction with gravity methods of applying the grit, inasmuch as under certain conditions, and for some purposes, it is desirable to employ both gravity and one of the forms of my invention in conjunction in order to attain a desired form of abrasive article.

In carrying out this invention, I find it desirable to employ a conveyor for conducting the mineral at rest relative to the conveyor by relatively slow speed to a point adjacent to which the independent force is applied for projecting the particles of grit onto the backing. I find that by then applying this independent force, be it mechanical or electrostatic or electro-magnetic, I am able to impart a high velocity to the particle so that any force of gravity acting on the particle, whether in the same direction, in a counter direction, or in a direction angularly to that at which the force is applied, will be relatively small compared to this force applied. It is possible with the present invention to apply the force directly counter to gravity, that is, by bringing the grits beneath the backing or by applying the force in some other direction as long as the force of gravity and the effect of air is reduced below a point which will interfere with the result desired, namely, the projection of the grits with their longitudinal dimensions ultimately perpendicular or substantially so with respect to the backing.

The principal objects and advantages of this invention reside in the provision of an improved abrasive coated article, such, for example, as sandpaper, emery cloth, or the like, wherein the abrasive grits or grains lie in position on the backing for increasing the cutting effect and durability of the abrasive article; the provision of an improved abrasive article wherein the abrasive grits are disposed so that their cutting facets are presented in position to more eiliciently engage the work and thereby produce a sharper article; the provision of an improved abrasive article wherein the abrasive grains or grits are applied thereto with their longer or greater dimension substantially perpendicular to the plane of the backing; the provision of an improved abrasive article which may be flexible or rigid, as desired, and which may or may not be made waterproof, that is, suitable for employment in a water abrading operation.

This invention further include as objects and advantages thereof, the pfovifion of an improved method of and apparatus for manufacturing abrasivearticles; the provision of an improved method of and apparatus for applying pulverulent material to one surface of a baclnng irrespective of the force of gravity, that is, against the normal tendency of the force of gravity; the provision of an improved method of and apparatus for propellin a pulverulent material, such as a grit or an abrasive grain against an adhesive coated surface; vthe provision of an improved method of and apparatus for the purpose set forth and including electrically operated means for act-' ing on an abrasive grain or pulverulent material and causing it to advance onto the adhesive coated backing irrespective of the force of gravity; the provision of an improved method of and apparatus for causing the particles of pulverulent material to impinge upon and assume a position in the adhesive coated surface substantially normal or perpendicular to the surface of the backing; the provision of an improved method of and apparatus for propelling a pulverulent material onto a moving sheet in a direction transversely to the plane of movement thereof and in a. direction substantially counter to-gravity; the provision of an improved method of and apparatus for makin abrasive articles, such as sandpaper and the like, which includes the application of a grit to the under side of the backing; theprovision of an improved apparatus which includes 'mean for feeding and applying a pulverulent material counter to the force of gravity and simultaneously with movement of the backing; the provision of an improved means for moving a web of paper and applying an adhesive thereto and including means arranged below and for operating synchronously with for applying a pulverulent material to theunder side of said moving backing; and the provision of an apparatus of the character described wherein improved electrostatic or electro-magnetic means may be employed, acting on the abrasive material and causing it to move at an accelerated speed toward the sheet so as to cause it to impinge thereon in the adhesive coating and thereby present the cutting edges of the abrasive grits away from the surface of the backing and thus increase the cutting ability and life of the abrasive article.

I have also found my invention useful as a mod-- ifying step in the employment of the conventional gravity process for applying grit in the manufacture of sandpaper or other abrasive and, therefore, additional objects of this invention reside in the provision of an improved method of interposing an additional step which will apply abrasive grains either before or after the application of grits by gravity in the usual manner, it being understood that the step of applying grit irrespective of gravity by an electro-magnetic or electrostatic means may be employed somewhere in the process of manufacture, the essential purpose being to increase the number of grits whose cutting facets are presented away from the backing and thereby to enhance the cutting ability of the finished article.

The apparatus of this invention includes a number of alternative forms for mechanically or electrically carrying out the steps of the process, and

to this end is provided an improved pneumatic means and improved vibrator structure for mechanically propelling the pulverulent material and improved electro-magnetic structure for act- 5 ing on the mineral and causing it to move in a cloud toward the adhesive coated surface of the movin web or backing. v

The foregoing and such other objects and advantages as may appear or be pointed out as this description proceeds are attained in the structures illustrated in the accompanying drawings in which:

Figure 1 is a schematic view illustrating one form of apparatus for carrying out the process of this invention;

Figure 2 is a view similar to Figure 1 of an alternative form of the invention;

Figure 3V is a further alternative form of the apparatus of this invention of employing mechanical vibrating means;

Figure 4 is an enlarged schematic view illustrating a portion of an abrasive article made in accordance with this invention;

Figure 5 is an additional form of apparatus for carrying out further steps of the process of this invention.

The method of the present invention includes as steps thereof the feeding of a web or strip of paper or other fabric at a predetermined rate of p d, pplying an adhesive substance to the under side of the sheet, or applying the adhesive coating to one side and then moving the sheet with the coated side out, and simultaneously with the movement of the coated sheet, causing a grit or abrasive material to be applied to this side. The sheet or web of paper may be moved so that the adhesive coated side is either presented downwardly or at any angle thereto. The movement of the abrasive grains onto the under side of the backing is done irrespective of the force of gravity and, in fact, directly counter to gravity, and preferably done by imparting relatively high velocity to the abrasive material, thus causing it to impinge upon the adhesive coating. In view of the fact that the abrasive grains are projected through an intervening space from a suitable carrier onto the adhesive coated side irrespective of or counter to the force of gravity, the grains, which are usually somewhat elongated, will assume a position in transit so that the longer dimension thereof will take a position normal to the surface of the backing, thus causing the grains to stand on the surface rather than lie flat in greater percentage than when they are deposited by gravity. It is to be understood that this movement ofthe grains and deposition of them on the coated surface may be carried out in a number of ways, either by vibration, by an air blast, or by electrostatic or electro-magnetic means.

In the alternative forms of this invention later to be described, the method involved includes combining a gravity deposition of mineral on the adhesively coated moving backing with the Step of applying the grits irrespective of gravity, this being particularly useful in some of the heavier grits wherein it may be found that the force susceptible of applicationby an electrostatic or an electro-magnetic means is not sufficiently active on the available area of the individual grits to cause an entirely satisfactory result or to move enough of the grits onto the sheet to attain the desired end. In this invention it may be required to apply some of the grit by gravity and later apply someof the grit by one of the methods or asvasss 3 this invention or vice versa, but, in any event, the number of grits in the entire finished article which stand erect on the backing will be measurably increased over the ordinary methods heretofore employed for depositing grit on a backing for forming an abrasive article.

This invention produces a very satisfactory piece of sandpaper in which the cutting ability is measurably increased and by the deposition of the grains of sand or grit irrespective of the force of gravity, it is possible to produce an orientation of the mineral as desired and to control the thickness of the abrasive coating much more readily than where gravity alone is relied upon or employed for depositing the rains on the sheet.

Referring now more particularly to Figure 1;

the flexible backing of paper or cloth or other fabric is trained or fed over a series of rollers 0, I, and over one of a pair of the squeeze rollers, indicated at 'l, the other roller 8 of said pair being in contact with an adhesive material contained in a tray or tank 9 by which an adhesive coating is applied to one side of the moving web. After receiving the adhesive coating, the web I. is trained over rollers l0 and I I and is brought back over a roller l2 so that the adhesive coated surface of said web is presented downwardly. The web may then be trained over rollers I3, I l, and

' fed to a suction drum ll, whence it passes into festoons for drying.

The mineral is supplied from a hopper l6 and a conventional outlet H which feeds a layer ll of mineral to a moving conveyor is. This conveyor I9 is preferably porous and passes over the feeding rollers 20 and 2| and is adapted to move at a suitable rate of speed to supply a sufllcient quantity of abrasive grain. In some cases, it has been found-advantageous to move the conveyor at a speed substantially the same rate of speed as the web it, although these speeds are, of course, variables. The rollers 20 and 2| are mounted in the ends of a suitable frame 22, and this frame may be raised and lowered so as to vary the distance betweenmineral conveyor [9 and the moving web l5. This frame 22 may be supported fixedly at one end, as indicated at .23, and the other end may be raised and lowered by a toggle arrangement 2! activated by a threaded rod 25. Below the conveyor I 9 and at the movable end thereof, that is, adjacent to the web l5, there is provided a second conveyor 26 which serves to conduct away excess mineral which flows over the end of the conveyor I 9 and which may be returned in any suitable manner to the mineral hopper.

Below the upper flight of the conveyor 19, there are provided two air troughs 21. These air troughs are provided with flat upper walls 28, having slots 29 therein, said slots extending across the width of conveyor l9 and the troughs themselves being connected to a suitable source of air under pressure.

These troughs form in effect elongated jets or nozzles and when so placed below the conveyor belt or frame 22, a small quantity of air is emitted at high velocity which passes through the porous belt or conveyor.

that the mineral is caused to strike into the adhesive at a relatively high velocity and become impinged therein. Owing tothe projecting of the mineral in this manner through the intervening air space, the individual particles of grit or abrasive material are caused to assume a position parallel to their trajectory, that is, with their longer dimension perpendicular to the surface of the flight II. In view of the fact that most of the particles of mineral are somewhat elongated, due to the manner of production of the same, they will naturally assume this position in movement from th conveyor I! to the adhesive coated surface of the backing. As they arrive at the adhesive material, they impinge themselves thereon and will thus stand erect in the adhesive, thus forming a sharper contour for abrasive purposes. By varying the rate of speed of the moving backing relatively to the speed of the conveyor and by varying the distance between the conveyor and the backing and the velocity of the air stream, and by increasing or reducing the number of such jets and the quantity of adhesive applied, any reasonable desired thickness of grit layer may be produced during the process and without stopv be dumped into the conveyor 26 and returned by any suitable means to the hopper I.

Referring now to Figure 2, there is provided the same general arrangement of moving backing, having the flight 30 adhesively coated from the squeeze rollers 3|.

Below the flight 30 there is provided a mineral feeding conveyor Isa, receiving pulverulent material from the hopper lta.

The conveyor He is mounted for movement toward and away from the flight 30 similar to the conveyor is and. therefore, this structure has not been shown in Figure 2.

As the mineral flows from the hopper ISA it does not always assume a smooth or even distribution on the conveyor ISA, and, therefore, it may be desirable to provide a pair of charged electrodes 32, one arranged above and one below the conveyor ISA, for the purpose of spreading the mineral evenly on the conveyor belt. The conveyor ISA in this instance may be non-porous.

when charged electrodes are put in this position they act in princi le the same as the charged electrodes used for coating the mineral on the backing. An electrical charge or difference of potential is set up between the electrodes 32. The voltage or difference in potential between those electrodes is maintained great enough to produce a, strong static field, but not so great as to break down the insulation between the plates, which insulation may be the dielectric strength Of the air or the dielectric strength of the air plus the dielectric strength of any insulating material which may be used to wrap the electrodes.

As the mineral on the conveyor enters the static field between the plates the mineral particles take on the charge of the lower plate, and are repelled to the upper plate where they lose their charge and take on the opposite charge of the upper plate. At this point they are repelled to the lower plate. Since new mineral is being conveyed by the conveyor into the field continuously the static fields soon become supersaturated with mineral particles. and an equilibrium is reached where as many particles are thrown out of the static field as are brought in by the conveyor. By having a down-turned end 32A of the upper electrode the mineral particles that 'are thrown out of the static field are deflected evenly on the conveyor belt so that a smooth the time it is being coated, streaks, thin spots, etc.,

in the finished product are reduced.

At the same approximate point at which troughs 21 are provided in Figure 1 there are here provided electrically charged electrodes 33 and 34,

the electrode 34 .being located below the upper flight of the conveyor belt ISA and electrode 33 being disposed above the flight 30 of the backing. A suflicient difference of potential is maintained at electrodes 33 and 34 to produce a strong static field, similarly to that referred to above. This static field moves the mineral from the belt ISA to the underside, which is the adhesive coated surface of the flight 30.

As the mineral enters the static field between the electrodes 33 and 34 it becomes charged with the charge of the lower plate, and is here propelled to the upper plate 33. r

It will be observed that in this method of coating the mineral is applied by a force other than gravity. In all other methods of coating sandpaper, known to me, the velocity of the particle is either in whole or part given to it by the force of gravity. In the case of this electrostatic.

coating the particles are oriented in the static field so that there is a tendency for the long dimension of the mineral to be perpendicular to the electrode plates, and also perpendicular to the web 30, whichis being coated, The finished sandpaper product, therefore, contains a substantial percentage of the particles of mineral standing on end rather than laying flat, thereby increasing the cutting properties of the abrasive article.

Excess mineral is dumped onto the conveyor 35, whence it may be returned to the hopper I60.

Referring now to the form of the invention shown in Figure 3, the moving web 55 is trained over a series of rollers similar to the arrangement shown in Figures 1 and 2 so that a horizontal flight 51 of the paper backing is provided, having an adhesive coating on the under side thereof. Squeeze rollers 58 engage the paper backing for applying an adhesive thereto.

In this form of the invention, a mechanical vibrating means is provided which serves to propel the mineral, that is, the grit, from the gritfeeding conveyor 53, which latter receives mineral from the hopper 60, having a gate 6|. The conveyor 59 is trained over rollers 62 and 63 mounted in a suitable frame 64, which latter may be mounted for adjustment toward and away from the flight 51 similarly to the conveyor IQ of Figure l. The conveyor 59 extends below and is separated from the flight 51 of the paper web and travels at substantially the same speed as the I paper web.

The conveyor 59 passes between sets of pinch rollers, one above and one below the upper flight of the conveyor 59 as indicated by 65 and 55, and also beneath a pinch roller 61 which bears on the roller 62. The pinch rollers 65 and 66 tend to distribute the mineral evenly over the surface of the conveyor and are so spaced from the rollers 52 and 51 that the portion of the belt 59 between the rollers 65 and 66, and 62 and 61 is permitted to lie slack, whereas the remaining part of the conveyor is substantially taut. This arrangement tends to limit the vibration of the conveyor belt to the zone 01' application of the mineral to the paper backing. as indicated at 68.

Beneath the portion 88 of the belt 53, there is provided a revolving Ibatter 83 operating on a shaft carried in suitable bearings in the frame 64 and provided with a plurality of radial arms 10 which upon rotation rigidly strike the under side of the portion 68 of the belt, thus throwing or pro- Jecting the mineral content thereof against the under side of the adhesive coated paper backing, much in the manner in which the air stream blows the mineral or grit against the paper backing as shown in Figure 1. The batter 83 may be driven in any desired manner from a separate source of power or may be connected suitably with the rollers driving the belt 59, but geared to operate at a greater rate of speed. The rollers 65 and 66 and the roller 61 are separately driven from the belt 53 so as to produce the tautness in 21819 belt, except the flight of the belt indicated at In Figure 4, there is illustrated an article made in accordance with the present invention. The

backing is shown at to which an adhesive coating 8| has been applied, and the grits, greatly enlarged, are indicated at 82, and it is noted that they stand on end in the adhesive coatin thus causing their sharper edges to project beyond the upper or outer surface of the coating, thereby enhancing the cutting ability and increasing the life of the abrasive article. While the article shown in Figure 4 is purely schematic, it will be understood that the mineral actually does take a position substantially normal to the backing and, while all of the grits may not take this position, a large number of the same do, and the cutting qualities of the abrasive article are thus greatly increased. Furthermore, by so disposing the grits, it permits of the application of an additional sizing coat or coats to the back and to the front or cutting face of the abrasive material without completely burying the grits and as a thicker coat of adhesive may thus be employed on the cutting face of the abrasive material, the engagement of v the adhesive material with the abrasive material is greatly enhanced, thus further tending to increase the life of the abrasive article. Such a sizing coat is indicated at 83.

As previously pointed out, where the electrostatic or electro-magnetic methods are resorted to in some of the coarser grades of abrasive devices made, it may be found that the electrostatic or magnetic field into which the particles are conducted may not exert on each individual particle suflicient force to cause proper orientation of the particles, for the reason that the static eifect is substantially proportional to the area of the particle, and the coarser the particle, the smaller the area of eifect per weight. Therefore, as larger grits or sizes of particles are employed, increased force is required to move the particle, and for some purposes, insuflicient increase in force results because of the reduced area per weight. Therefore, in such cases, a form of the invention, as shown in Figure 5 may be resorted to wherein the mineral is applied to the adhesively coated backing in part by gravity and in part by electrostatic or electro-magnetic means.

In view of the fact that the electrostatic and electro-mag'netic means may for some purposes Referring in detail to Figure 5, I have illustrated a. web of paper 84 coming off a roll 85 and passing through an adhesive coating device illustrated in general at 86. The web 84 is thence trained over rollers 81, 81a, so that it has a sub-- stantially horizontal flight 81b, which receivesgrits in the desired amount from an ordinary conveyor 80 said conveyor receiving grits from the hopper 19. The web of paper thence is carried downwardly to a horizontal flight 99 by the provision of rollers 9i, 9|, and an electrostatic or electro-magnetic or other grit applying means for applying grit counter to gravity may be employed at one or more points as indicated at A and B, wherein the conveyors I and IOI convey grit from suitable hoppers I02 and I03, and electrodes I04, I04 and I05, I05 serve to apply the grit.

As the web passes over the rollers 81a and 9|, a quantity of the mineral deposited from the conveyor 88 onto the web will drop off, and, for conveying away this excess mineral, I provide a transversely running conveyor 92a arranged between the fiight 99 and the conveyor I00.

It will be understood that while the electrostatic and electro-magnetic means for coating counter to gravity are illustrated in Figure 5, the mechanical means hereinabove described may be conveniently employed in these locations without departing from the spirit of the invention. However, the reason the electro-magnetic and electrostatic elements are particularly mentioned here is that the difficulty of counter coating successfully with the coarser grains is more.likely to arise with these elements than with the vibrator or air blast heretofore described.

I wish to point out that where the expressions "electro-magnetic and electrostatic are employed in the specification, I refer to the employment as well of a permanent magnet or some other form of static charge or magnetic charge which will erform the function.

Having thus described my invention and illustrated its use, what I claim as new and desire to secure by Letters Patent is:

1. The method of coating a backing with elon-' gated particles of material which includes the step or steps of first applying a coating of adhesive to a surface of said backing, then successively impinging increments of said particles against said adhesive coated surface until a plurality of successively applied increments have been deposited on the adhesive, the particles of at least one of said increments being coated on said surface by applying a propelling force, acting to project particles upwardly against the force of gravity from a preliminarily distributed layer spaced from said surface of said backing, and to direct the particles into contact with said adherality of successively applied increments have been deposited on the adhesive, the particles of at least one of said increments being coated on said surface by applying a propelling force, acting to project particles upwardly against the force of gravity from a preliminarily distributed layer spaced from said surface of said backing, and to direct the particles into contact with said adhesive coated surface, the propelling force being generated by an electrostatic field and said layer being distributed upon a movable carrier spaced from said backing and moving through said field.

3. The method of coating abacking with particles, of material which includes the steps of applying a coating of adhesive to a surface of said backing and applying the particles of said I material to said adhesive coated surface in a lurality of successively applied increments thereof, the particles of at least one of said increments of material being propelled upwardly against the force of gravity into contact with said adhesive coated surface of said backing from a preliminarily distributed layer of said particles of material spaced from said surface of said backing by applying to particles in said layer, a propelling force generated by an elestrostatic field, within which field said particles of said layer are disposed.

4." In apparatus for coating particles of elongated material upon a backing, the apparatus comprising in combination, means for providing adhesive to said backing arranged to unite said material to said backing, at least one movable carrier for providing said material in a layer spaced from said backing, and means for propelling said material upwardly against the force of gravity comprising a plurality of successively arranged pairs of opposed electrodes creating successively effective electrostatic forces between said spaced electrodes, and means for passing said backing successively between said successively arranged pairs of electrodes, whereby as the backing passes between said electrodes, the adhesively coated backing is impinged by a plurality of succesively applied increments of said material.

.5. In apparatus in accordance with claim 4,

wherein said opposed electrodes are plates which achieve orientation of a substantial number of the particles substantially normal to the plates and the backing which is passed between the plates.

6. In apparatus for coating particles of material upon a backing, in combination, means for applying adhesive to said backing to hold said particles to said backing, means for propelling said particles upwardly against the force of gravity from the surfaces of movable carriers therefor to a surface of said backing coated with 'said adhesive, comprising a plurality of successively arranged pairs of spaced electrodes creating successive electrostatic fields, and means for passing said backing successively through said electrostatic fields between said electrodes and in spaced relation to said carriers whereby a plurality of separate increments of said particles of material are successively-applied to said adhesive coated surface. of said backing.

PAUL CARLTON.

CEnTIFICA'EbF come-non.- Patent 210. 2,576,515. May 22, 191

- RICHARD PAUL CARLTON.

It is hereby certified that error appears in the above numbered patent requiring correction as follows: In the heading to the printed specification, line 7, strike out the word "Application" and insert instead -Contimmtion of application Serial No. 1422,065, January 20, 1950. his appli cation-; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 16th day of October, A. D. 1915.

Les11e Frazer (Seal) First Assistant Commissioner of Patents 

